1. Field of the Invention
This invention relates to the separation of materials by magnetic techniques. More particularly, this invention relates to the separation, or precipitation, of materials having very low positive or negative magnetic susceptibility. In one important aspect, this invention relates to the magnetic precipitation of diamagnetic materials, such as biological materials, human bone particles, and so forth.
2. Description of the Prior Art
The use of magnetic techniques for separating ferromagnetic materials from background substances has been known for quite some time. Recent refinements of such techniques have made it possible to precipitate hyperfine ferromagnetic wear particles from a lubricant sample taken from a machine, such as a diesel engine, and to determine the wear condition of the machine by optical analysis of such particles. A detailed description of apparatus and procedures for performing such precipitation and analysis is set forth in U.S. Pat. No. 4,047,814, issued on Sept. 13, 1977 to Veron C. Westcott.
In accordance with that prior disclosure, a lubricant sample is caused to flow along a shallow channel in a nearly horizontal glass substrate positioned over a magnet the air-gap of which is aligned with the longitudinal axis of the substrate. The magnet develops in the vicinity of the substrate, along the lubricant flow path, a magnetic field having a very high gradient perpendicular to the substrate surface. Ferromagnetic wear particles are drawn by magnetic force down from the lubricant liquid so as to precipitate onto the substrate surface.
In carrying out this procedure with ferromagnetic wear particles, the larger particles are precipitated first, and the smaller particles are precipitated further along the flow path. Analysis of the relative proportions of large and small size wear particles provides significant information about the state of wear of the machine from which the lubricant sample was taken. Similar techniques can be used to precipitate non-magnetic particles which wear against a ferrous metal such as steel, since the ferrous metal smears on or becomes embedded in the non-magnetic material which thus becomes effectively magnetic.
There are many occasions when it is desired to separate essentially non-magnetic particles which have not worn against a ferrous metal. Some of these materials are diamagnetic (popularly considered non-magnetic) and are weakly repelled by a magnetic field. Included in such materials of interest are wear particles from human joints, microscopic organisms, wear particles from plastic against plastic, ceramics, etc. It also is desired to precipitate weakly paramagnetic materials, such as aluminum, which are attracted towards an increasing magnetic field but with such a small force that the materials are usually considered non-magnetic.
Accordingly, it is an object of this invention to provide improved techniques for separating or precipitating by magnetic means materials which are essentially non-magnetic. A more specific object of the invention is to provide techniques for separating diamagnetic materials from various background substances. Other objects, aspects and advantages of the invention will in part be pointed out in, and in part apparent from, the following description of preferred embodiments of the invention.
In the following description, the term magnetic susceptibility is used in the usual sense, as the ratio of the intensity of magnetization produced in a substance to the magnetizing force or intensity of field to which it is subjected. Materials exhibit a wide range f susceptibilities.
A technique is described for imparting to some materials a relatively high positive susceptibilitiy. Materials that respond by developing the high magnetic susceptibilities are defined as susceptic materials.